Firstly, what agent is your library set up to use?
Trying to use the Plex Movie agent in Fix Match on a library that isn’t configured to use the Plex Movie agent will not work. You can however use the legacy Plex and TMDB agents to Fix Match if your library is using the new Plex Movie agent. There is some work that still needs to happen in the web client to prevent you trying to match to the new agent when you’re using legacy agents.
You rarely should ever need to use Fix Match though if the files are named correctly, if you find that you need to do this often then there is likely some other underlying problem (or you have some really obscure titles in your library).
